Ester and ketone enolates of Ti, Zr and Hf are either known compounds or are obvious from the art. Moreover, the use of Ziegler-type coordination catalysts for the polymerization or copolymerization of non-polar 1-olefins, such as ethylene or propylene, is well known in the art. Such catalysts usually are based on transition metal salts, e.g. titanium, zirconium or vanadium halides, which have been converted into reduced valence states by reaction with a variety of alkylating or arylating substances, usually simple organometallic compounds of a metal of Groups I, II or III of the Periodic Chart of the Elements. More recent variants of Ziegler-type catalysts employed in olefin polymerization include those described in U.S. Pat. Nos. 3,681,317, 3,740,384, 3,738,944 and British Pat. No. 1,314,828 wherein tetrabenzyl-transition metal compounds, e.g. tetrabenzyl zirconium, are complexed with anionic ligands, e.g. halide, and/or neutral ligands, e.g. pyridine. U.S. Pat. No. 3,773,742 discloses tetraneopentyl titanium as an ingredient in an olefin polymerization catalyst, either alone or in combination with an organoaluminum compound or supported on silica gel. U.S. Pat. Nos. 3,971,767 and 35 3,950,269 disclose olefin polymerization catalysts comprising a suspension of alumina having chemically bonded onto its surfaces a transition metal hydrocarbyl hydride aluminate prepared by reacting a hydrocarbon solution of a tetra(hydrocarbyl) transition metal (R--CH.sub.2).sub.4 M, wherein R is non-beta H-containing aryl, aralkyl or tertiary alkyl, and M is Ti, Zr or Hf, with a suspension of a selected hydrated alumina. Polar monomers such as acrylic monomers may be included as minor comonomers.
U.S. Pat. Nos. 3,394,156 and 3,370,041 disclose the use of compounds of Ti or Zr as catalysts for the polymerization of acrylic monomers, including methyl methacrylate (MMA) and acrylonitrile. Included are compounds of the formula EQU (R.sup.1 R.sup.2 N).sub.a (R.sup.3 O).sub.b (BH.sub.4).sub.c MX.sub.d
wherein R.sup.1-3 are hydrocarbyl radicals, M includes Ti, Zr and Hf, X is an acid anion, which includes halogen, acetylacetonate and acetate, and a, b, c and d are zero or integers such that a+b+c+d=4.
U.S. Pat. Nos. 3,919,180 and 3,846,389 disclose the production of alternating copolymers of "donor" and "acceptor" monomers comprising not less than three monomers, in the presence of a catalyst prepared from (a) at least one compound of a transition metal selected from Groups IV and V of the Periodic Chart and (b) an aluminum-containing component consisting of one or more aluminum hydrocarbyl halides, at least one of (a) and (b) being complexed with a basic organic compound which is an organic nitrile, .alpha.,.beta.-unsaturated carboxylic acid ester, benzoic acid ester, selected amine or thiophene. Donor monomers are non-polar unsaturated hydrocarbons; acceptor monomers include acrylic monomers.
U.S. Pat. No. 3,114,737 discloses the aqueous dispersion polymerization of vinyl or acrylic monomers in the presence of: (a) a compound of the formula R.sub.n MR.sub.m ' wherein R is cyclopentadienyl, methylcyclopentadienyl, indenyl or fluorenyl, M is Zr or Ti, R' is alkoxy, cycloalkoxy, acyloxy or halogen, n is 1 or 2, m is 1-3 and m+n is 3 or 4; and (b) a co-catalyst comprising a halogenated acetic acid.
U.S. Pat. No. 3,037,004 discloses the liquid phase polymerization of acrylic acids, acrylates, alkyl styrenes and acrylonitrile with a catalyst comprising (a) the Zr or Ti compound of U.S. Pat. No. 3,114,737, provided that when m is 3, at least one R' must be halogen or acyloxy, and (b) a ketone or aldehyde whose carbonyl group is not in an aromatic ring.
European Patent Application Publication No. 0 017 937 and Japanese Patent Application No. J56 136,865 disclose polymerizable medical or dental bonding compositions comprising a (meth)acrylate or (meth)acrylamide monomer and a selected Ti or Si compound; the titanium compound is of the formula EQU R.sub.6 O--Ti(OR.sub.3)(OR.sub.4)(OR.sub.5)
wherein: R.sub.3 is C.sub.1-20 aliphatic hydrocarbyl optionally with one or two OH groups, C.sub.1-3 alkoxy or di(hydroxyC.sub.2-3 alkyl)amino; and R.sub.4-6 are hydrocarbyl optionally with one or two OH groups; or R.sub.7 CO-- wherein R.sub.7 is olefinic hydrocarbyl CH.sub.2 .dbd.CR.sub.8 -- wherein R.sub.8 is H or CH.sub.3, C.sub.1-20 saturated hydrocarbyl optionally with one or two OH groups, C.sub.1-3 alkoxy or --COR'.sub.8 wherein R'.sub.8 is C.sub.1-3 alkyl. For polymerization the composition, preferably in two parts, also contains a catalyst and an activator, which are exemplified by N,N-bis(2-hydroxyethyl)-4-methylaniline and benzoyl peroxide, respectively.
Japanese Patent Application No. J61 026,606 discloses the polymerization of ethylene and an acrylate in the presence of a Lewis acid and a catalyst comprised of compounds of the formula EQU M.sup.1 (OR.sup.1).sub.l X.sub.m Y.sub.n (a)
and EQU R.sup.2.sub.q M.sup.2 X.sub.p-q (b)
wherein: M.sup.1 is V, Zr or Hf; R.sup.1 and R.sup.2 are C.sub.1-20 alkyl, cycloalkyl, aryl or aralkyl; X is halogen; Y is oxygen, cyclopentadienyl or acetylacetonyl; M.sup.2 is Li, Na, K, Zn, Cd, Al, B or Ga; l, m and n are 0-5; p is the valence of M.sup.2 ; and q is &gt;0 and equal to or less than p.
U.S. Pat. Nos. 4,414,372; 4,417,034; 4,508,880; 4,524,196; 4,581,428; 4,588,795; 4,605,716; and 4,622,372, and commonly assigned U.S. patent application Ser. Nos. 660,588 filed Oct. 18, 1984; 771,684-771,686 filed Sept. 3, 1985; 786,101 filed Oct. 15, 1985; and 872,610 filed June 10, 1986, referred to hereinafter as "the aforesaid patents and patent applications", disclose processes for polymerizing a polar acrylic or maleimide monomer to a "living" polymer in the presence of an initiator, which is a tetracoordinate organosilicon, organotin or organogermanium compound having at least one initiating site, and a co-catalyst which is a source of bifluoride, fluoride, cyanide or azide ions or a suitable Lewis acid, Lewis base or selected oxyanion. Such polymerization processes have become known in the art as Group Transfer Polymerization (Webster et al. J. Am. Chem. Soc. 105, 5706 (1983)).
M. T. Reetz, "Selective Reactions of Organotitanium Reagents", Pure and Appl. Chem., 57, No. 12, December, 1985, pp. 1781-1788, discloses that titanium ester enolates in the absence of a catalyst cause rapid oligomerization to produce living polymers in quantitative yield. An unbalanced chemical equation indicates reaction of 1-tris(isopropoxy)titanoxy-1-methoxy-2-methyl-1-propene with methyl methacrylate to form a 1:1 adduct which then forms polymer. No process details are provided and there is no indication of reaction conditions, such as temperature, solvents or reactant ratios necessary for polymerization.
It is an object of the present invention to provide processes for preparing "living" polymers by polymerizing one or more acrylic monomers in the presence of an organotitanium, organozirconium or organohafnium polymerization initiator. A further object is to provide "living" polymers containing initiating sites comprising the aforesaid metals. Another object is to provide such "living" polymers as intermediates to useful linear or branched acrylic polymers, including block copolymers, optionally containing functional substituents for further chemical processing. These and other objects will become apparent from the description which follows.